The sickest patients in the community are recently hospitalized elders. A substantial component of their morbidity and mortality is caused by adverse drug events (ADEs). ADEs account for 70% of adverse events occurring after discharge, which occur at a rate of 0.30 ADEs per patient. The oldest, sickest patients are at highest risk for ADEs because they have the most complex and hazardous medication regimens yet the least physiologic reserve and the fewest social and economic resources. Several studies, including our own, have demonstrated the efficacy of pharmacist-led post-discharge interventions to improve medication management. Most prominent among these have been post-discharge phone calls from pharmacists to patients. However, despite demonstrated efficacy, these interventions have not been widely implemented. In this proposal, we use the RE-AIM model to understand and address gaps in existing research that have hindered implementation. The central knowledge gap is that most research focuses on process or surrogate endpoint measures (like medication discrepancies) that we now understand to be insufficient to motivate organizational change. In contrast, we will measure the effect on utilization, a closely-tracked outcome that strongly motivates hospital leaders. We will use a large randomized controlled trial to rigorously assess the effect of PHARM-DC on this outcome. We will also study the barriers and facilitators of adopting these interventions, about which little is known. Finally, although implementation costs are critically important information for organizations considering pharmacist-led discharge (PHARM-DC) interventions, evidence on this topic is scarce. We thus aim to measure the impact of PHARM-DC interventions on post-discharge utilization within 30 days. We will also identify patient sub-populations most likely to benefit from PHARM-DC. Finally, we will estimate the incremental net cost of PHARMs from the health system perspective. To study these aims, we have selected two sites that: 1) are already proficient at in-hospital medication reconciliation, a prerequisite for implementing and evaluating PHARM-DC; 2) have a Chief Pharmacy Officer committed to using operational resources to provide PHARM-DC to patients during the study period; and 3) have investigators experienced in the research content and methodologies needed to study the aforementioned aims. This project will generate new knowledge allowing for increased implementation and dissemination of research already known to be efficacious, thus reducing the substantial morbidity and mortality attributable to ADEs among seniors in the high risk post-discharge time period.